toliet waste in 2nd bathroom!!

can anyone help - I have two back-to-back bathrooms and whenever I flush the ensuite toliet, waste from there ends up in the 2 nd toliet - yuk!! anyone experienced this before or can give advice. I'm a complete amateur so need basic info. thanks!

Theoretically it should not be able to happen, so you either have a drain problem or a poor pipe installation problem. We cannot tell which without checking your situation. But if I remember correctly, the strike was ended by the 70's.